The conventional numerical control apparatus involved making individually a contour control, to control a contour along which a workpiece is cut, in the X-Y axis direction and a chopping control for effecting the reciprocating movement at any period and amplitude.
Therefore, when the chopping control process was performed in the reciprocating movement at any period and amplitude in accordance with a commanded pulse, using the numerical control apparatus, a machine tool (e.g., grinding machine) controlled by this numerical control apparatus additionally had a chopping dedicated axis (chopping axis), other than the normal control axis (X axis, Y axis and so on).
When this machine tool is employed under the chopping control of the numerical control apparatus, the necessary information for the chopping operation, such as the amplitude (positions of top dead point and bottom dead point) and the reciprocating movement period necessary for the chopping control, are set in advance as the parameters. Then, the chopping axis (e.g., about which the grinding stone is operated) is positioned vertically along the Z axis for the contour locus on the X-Y plane (horizontal plane), and reciprocated in the Z axis direction, in which a table with the workpiece laid is moved in the X-Y axis direction along the control axis to make the contour control, so that the chopping control process is performed with the contour commanded in the processing program, as shown in FIG. 10.
Also, when the chopping control process was performed in a state where the processing face of the workpiece was inclined, as shown in FIG. 11, using the numerical control device, the machine tool was provided with a rotatable chopping axis for making the chopping operation in the state where the workpiece was inclined at a predetermined angle and a rotation axis (C axis) around which the grinding stone was rotated perpendicularly to the processing face on a mechanism for moving the grinding stone along the control axis in the X-Y axis direction.
The machine tool as shown in FIG. 11 performs the chopping control process by making the reciprocating operation and rotational operation for the workpiece (chopping axis) in the arrow direction in the state where the workpiece is inclined, as well as causing the grinding stone held perpendicular to the processing face by rotating the rotation axis (C axis) to be moved in the arrow direction by adjusting the control axis in the X-Y axis direction.
By the way, the conventional numerical control apparatus performed individually the contour control in the X-Y axis direction and the chopping control for making the reciprocating operation in any direction at any period and amplitude, as described above. Therefore, the machine tool with the conventional numerical control apparatus capable of the chopping control process required a dedicated chopping axis for realizing the chopping operation in the reciprocating movement, separately from the control axis for contour control.
Also, in the machine tool with the numerical control apparatus for realizing the chopping operation in any oblique direction as shown in FIG. 11, the rotation axis (C axis) for rotating the tool perpendicularly to the processing face was required, other than the dedicated chopping axis.
In this connection, in the machine tool with the numerical control apparatus capable of the chopping control process, the machine constitution having the chopping axis mounted on a group of contour control axes is required, resulting in a problem with the adjustment or maintenance for the complicate mechanical constitution.
Also, in the machine tool for realizing the chopping operation in any oblique direction as shown in FIG. 11, the rotation axis (C axis) is further required other than the chopping axis. Hence, various problems arise with the manufacturing cost and superposition in the mechanical aspect, as compared with the machine as shown in FIG. 10.
Moreover, since it is permitted to correct the chopping operation for an error (e.g., when the period is faster, the actual amplitude is shorter than the predefined amplitude due to a delay of servo control) only with the chopping axis, there was a problem on the control that it was difficult to correct the chopping operation for a movement error in the contour control with the positioning axis or rotation axis.